1. Field of the Invention
This application relates to cannulae and, in particular, to cannulae having reduced flow resistance and a tip configured to redirect the flow of fluid out of the cannula.
2. Description of the Related Art
Treatment and diagnosis of a variety of health conditions in a patient can involve withdrawing blood from and returning blood to a patient's vascular system, e.g., in treatment of organ failure. In dialysis treatments, which are sometimes applied to patients suffering from kidney failure, blood is withdrawn from the vascular system, filtered, and infused back into the vascular for further circulation. An emerging treatment for congestive heart failure involves coordinated withdrawal of blood from and infusion of blood into the vascular system. Both such treatments sometimes call for the insertion of cannulae into the vasculature of the patient.
It is sometimes beneficial to access the vascular system by way of a single entry point using a multilumen cannula. Multilumen cannulae enable blood to be withdrawn from the vascular system via a first lumen and infused back into the vascular system via a second lumen. By providing vascular access through a single point, multilumen cannulae are less invasive than other options for coordinated aspiration and infusion, such as the insertion of multiple single lumen cannulae through separate entry sites.
Though multilumen cannulae advantageously can limit the number of entry sites, the size of the lumens of such cannulae are limited by the need to fit more than one lumen into the same region of a vessel. Small lumens can suffer from high flow resistance, especially if relatively long. Increased flow resistance of the lumens of multilumen cannulae present many problems for the devices that are coupled with the cannulae to direct blood into or withdraw blood from the vascular system.